Thermal fuze



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May 24 1960 J. M. Mr-:EK ETAL 2,937,596

THERMAL Fuz Filed 0G13. 2. 1958 JAMES M. )WEEK RAYMOND WARRE N ATTORNEY-5 United States Patent C THERMAL FUZE .lames M. Meek, Silver Spring, Md., and Raymond W. Warren, McLean, Va., assignors to the United States of America as represented bythe Secretary of the Army Filed Oct. 2, 1958, Ser. No. 765,011

Y 4 Claims. (Cl. 102-70.2)

(Granted under Title '35, U.S. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment to us of any royalty thereon.

This invention relates generally to a thermal fuze which is activated by heat resulting from air passing over the outer surface of aflying missile.

Detonation of a missile warhead by a fuze is accomplished by the application on the part of the fuze of an electrical pulse or a mechanical impulse to the missile warhead. When the missile is required to explode at `some predetermined point relative to the target, the time of detonation must be accurately controlled in order to insure that the missile is within lethal range of the target. Initiation of detonation of the warhead at some predetermined point relative to the target has been accomplished by proximity fuzes of various types. However, the disadvantage of using proximity fuzes to initiate detonation is that they are complex and expensive. In fuzing .applications it is desirable that the fuze be neither cornplex'nor expensive and yeti be capable of accomplishing accurate timed detonation ofthe missile warhead at some predetermined point relative to the target, 'so that air bursts can be `attained if desired.

' One ofthe inevitable'consequencesof high. speed missile'` flight is that friction created'by air passing vover `the skin or outer 'surface' ofthe missile Vincreases the temperature of the skin to a considerable extent.' rIhis phenomenon is generally known to those in the art as c aerodynamic heating. It has been found' that'V for any t particular type of missile' having `known flightand velocity characteristics, the aerodynamic heating of the missile skin at any point during the'time of llight of the missile can be accurately predicted or determined from test missiles. of thef same type.

' Itis the purpose' ofthis invention to utilize the-predictaible heatingiofA the skin to accomplish initiation of detonation ofthemssile by` an inexpensive and relatively simcloses: the"switch1 and thereby initiates detonation of the missile."A

Still another object of this invention is to provide a `thermal-activated switch systemwhich responds to a condition of heat to initiate detonation, but which will function satisfactorily after launching, even though the missilezwith'the system incorporated therein has been previously subjected to accidental heating.

According to'this invention a thermal fuze is provided which initiates detonation of a missile aftersetback, as

a resultof aerodynamic heating Aof a thermal. motor in the-fuze. The1 thermal motor includes a vaporiz'able 2,937,596 Patented May 24,7k 1960 ICC liquid encapsulated within a sealed expansible bellows.

of heat conducted to the liquid will cause th'e liquid to develop sufficient vapor pressure to expand the bellows which drives means capable of initiating detonation of the missile. The predetermined quantity of heat is created by missile iiight and is attained at some predictable period of time during the ight of the missile towards the target.

The specific nature of the invention, as well asl other objects, uses and advantages thereof, will clearly appear from the following description and from the accompanying drawing, in which:

Figure 1 is a sectional side elevation of the thermal motor and associated switch.

Figure 2 is a sectional view taken through lines.I 1--1 of Figure l.

Referring now to Figure 1, there is shown one embodiment of the thermal fuze of this invention. Thermal fuzing mechanism 10 is designed to be fixed Vin a fuze well (not shown) in the missile M. The v`body 12 of thermal fuzing mechanism 10i has a bore 12a in which cylindrical rod 21 can slide longitudinally. The end `(of body 12 nearest the center of the missile is provided with two sockets 14 into which prongs 16 of contact holding member 15 can be tightly inserted so as to align and position body 12 relative to the contact holding member 1S.

Contact holding member 15 is fixed withinthebody of the missile M and includes two electrical conducting rods 17 which are electrically insulated from member 15 by cylindrical insulating sleeves 18. The contact ends 17a of rod 17 extend slightly above the surface of member 15 and are positioned so as to be shorted by metallic sleeve 22, which is wrapped around the innermost end of rod '21, as shown in Figure l. When rod 21 is moved tothe position shown by the dotted lines in Figure l, sleeve.22 will complete an electrical connection between ends 17a. The opposite ends of rods 17 are provided with insulated nuts 17b which connect the ends of leadwires 13a` and 13b to the opposite ends of rods 17. Y

As shown in Figure l, lead wire 18a. is connected to one side of battery 19 while lead wire 18h is connected to setback-responsive switch 20. Switch 20 is designed to close by moving in the ydirection indicated byarrow A, in Figure 1, as a result of setback forces produced when the missile is tired or launched. Closing of switch 2l)V` as a result of setback locks the switch in the circuit and places battery 19in series with detonator Dand with rods 17. Subsequent connection of rods 17 by sleeve 22 causes battery 19 to initiate detonation of detonatorI D which causes detonation of the missile M. Movement of rod 21 to the dotted line position shown in Figure l is effected by operation of thermal motor 23.

Thermal motor 23 forms a unique and rel-atively simple v I means to accomplish timed detonation of the missile, and consists of a heat conductor 31, plate 29, bellows 27, and an encapsulated liquid 30. Conductor 31 is composed of a circular plate portion 24 and a cylindrical cup 24d which extends inwardly from side 28 of plate 24. The outermost surface of plate 24 is flush with the outer skin 11 of the missile so that `air passing over plate 24 when the missile is in flight will cause aerodynamic heating of the plate. Plate 24 has an inwardly projecting tiange 25, which makes point contact with smooth circular face 42 of body 12 and with an edge surface 32a of circular ring 32. Point contact between plate 24, body 12 andl ring 32 reduces the amount of heat conducted by conductor 31 to these parts. Ring 32 is externally threaded'and meshes with threaded ring 13 of body 12, thereby holding conductor 31 tightly in body 12.

Cylindrical cup 24a protrudes inwardly from plate 24,

as shown in Figure 1, with its longitudinal axis substantially perpendicular to the longitudinal axis of plate 24. Cup 24a receives heat which is conducted by plate 24 and rapidly conducts the heat so received through the thin walls of the cup 24a. The heat emanating from the walls of cup 24a increases the temperature of the area around the walls. Plate 24 and cup 24a are composed of brass or any other suitable heat-conducting material. The opening into cup 24a is closed by means of a plug 50 in order to prevent extraneous matter from falling into the cup.

The innermost portion of thermal motor 23 is composed of a circular plate 29 which is substantially coplanar with annular shoulder 26. Plate 29 is connected by welding or other known means to the outermost end of rod 21.

Positioned between plates 24 and 29 and surrounding the outer walls of cup 24a is an expansible bellows 27. The extremities of bellows 27 are sealed around the circumference of plate 29 and to thecircularV shoulder 26 of plate 24 by welding or brazing so that a vapor-tight seal is created by the bellows 27 between plates 24 and 29. Bellows 27 is substantially cylindrical and is coaxial to the longitudinal axis of cup 24a, -as shown in Figure 2. Bellows 27 can be composed of thin brass or steel or any other suitable expansible material. Encapsulated between bellows 27, plates 24 and 29, and the outer walls of cup 24a is a quantity of liquid 30.

As discussed above, when the missile is in iiight towards the target, aerodynamic heating occurs in conductor 31, and this heat is conducted to liquid 30 by means of the thin walls of cup 24a. For a particular type of missile M having a known velocity and trajectory, the time required -after launching for conductor 31 to attain a predetermined temperature by aerodynamic heating can be fairly accurately determined from skin temperature recordings obtained from test missiles.

As the temperature of conductor 31 increases, the vapor pressure of liquid 30 also increases thereby increasing the vapor pressure inside bellows 27. Plate 24 is xedly held to body 12 by ring 13 against possible movement caused by the increased vapor pressure. Plate 29 however, will be driven axially, i.e., in the direction of arrow B (Figure l), by bellows 27 when pressure developed inside the bellows is greater than the resultant forces preventing axial movement of plate 29. Reference will be hereafter made to the means for producing these forces.

It should be apparent to those skilled in the art that a given quantity of some vaporizable liquid such as dichloromethylene or carbon tetrachloride will exert an ascertainable vapor pressure against plate 29 when the quantity of liquid is heated by some quantity of heat for some constant period of time. Since the temperature of liquid 30 can be accurately predicted at any point in the flight time of a particular missile, the vapor pressure exerted by a given liquid in bellows 27 can be determined from vapor pressure and temperature tables. For a given suitable liquid, some substantially constant flight time is required before the quantity of heat conducted to liquid 30 by conductor 31 develops a vapor pressure in bellows 27 su'- cient to overcome the forces resisting movement of plate 29 and rod 21. Since the trajectory and velocity characteristics of any particular type of missile is known at launching, thermal motor 23 provides a relatively simple means to accomplish initiation of detonation at some predetermined point in the ight of the missile. An appropriate time delay can thereby be provided which causes the missile to detonate above the target at some predetermined height.

While dichloromethylene and carbon tetrachloride have been used successfully in the thermal motor, other liquids having suitable vaporization characteristics in a particular type of missile may also be used.

It is desirable if one size and type of thermal fuze can be used interchangeably in a number of different type missiles which have different velocities and trajectories and 4therefore different time intervals between the launching 4 and movement of plate 29 by the vapor pressure of liquid 30. The fuzing mechanism of this invention provides for adjustment of the pressure which can be exerted against movement of plate 29 caused by vaporization of liquid 30. By varying the pressure against plate 29, the time required before the pressure developed by vaporization of liquid 30 overcomes this force against plate 29 is also varied. Thus, one type and size mechanism can be interchangeably used in several different types of missiles.

The major forces acting against movement of plate 29 by bellows 27 in the direction of arrow B (Figure l) are produced by roller 34 and gear 37. Roller 34 ts in circumferential groove 33 in rod 21 and is biased inwardly towards the center of rod 21 by spring 35. Spring 35 is aflixed at its outermost end to fuze body 12 by rivets or any other suitable fastening means. Spring 35 forces roller 34 into engagement with the walls of groove 33, thereby restraining longitudinal movement of rod 21 towards the center of the missile-ie., in the direction of arrow B.

Rod 21 is also provided with a toothed rack 36 which is designed to engage teeth 37a of gear 37. Gear 37 is rotatably mounted by means of shaft 38 which is ixed at its ends in the missile M. Teeth 37a also engage a toothed rack portion 41a of shaft 41. The longitudinal axes of rod 21 and shaft 41 are substantially parallel. Shaft 41 is slidable in bore 40 and has a smooth portion 41b adapted to receive coil spring 43. The outermost end of spring 43 is retained by one end of member 44. Member 44 is slidable on shaft 45 and is limited in its outermost movement by cylindrical sleeve 46 which bears against body 12. Screw 47 is provided with a washer 48, and a washer retaining pin 49 which passes through and is held in the end of screw 47. When screw 47 is turned, member 44 will be moved by the rotation of screw 47 axially on shaft 4S towards shaft 41. Movement of member 44 in this direction compresses spring 43 and forces shaft 41 in the direction of arrow B. Circular rack portion 41a thereby produces a counterclockwise torque (as viewed in Figure l) on gear 37.

Movement of member 44 relative to shaft 41, as well as the tlexibility of spring 35, determines to a great extent the forces acting against movement of rod 21. When the exibility of spring 35 is kept constant, movement of member 44 provides a simple means for regulating the force acting against expansion of bellows 27 and movement of plate 29, and thereby provides a relatively simple means for varying the time required before the pressure developed by vaporization of liquid 30 finally drives plate 29.

Shaft 41 and gear 37 also serve the purpose of preventing accidental arming of the fuze switch should the missile be dropped so that the acceleration of rod 21 acting in the direction of arrow B overcomes the resistance to movement in that direction which is offered by spring 35 forcing roller 34 into groove 33. Sudden shock, with corresponding acceleration of rod 21, which might cause rod 21 to move in the direction of arrow B, also causes shaft 41 to move in the same direction. Shaft 41 moving in the direction of arrow B creates a counterclockwise torque on gear 37 which prevents movement of rod 21. Movement of rod 21 in a direction opposite to that shown by arrow B would not, of course, cause premature detonation of detonator D and consequent explosion of missile M.

The fuze mechanism of this invention requires the combination of a setback condition to close switch 20 and a condition of skin heating before detonation of detonator D occurs. Should the skin 11 and plate 24 be heated accidentally by a fire while the missile is in storage, thermal motor 23 might cause rod 21 to move to the position shown by the dotted lines in Figure 1. However,

since the additional condition of setback would not be present in such a case, premature detonation would not occur. Upon cooling, bellows 27 contracts until roller 34 drops back into groove 33. The missile can thereafter be safely handled and launched.

While the above-described embodiment is primarily i concerned with the closing of a switch so that explosion lof the missile can occur at some predetermined height above the target, it should be evident to those skilled in the art that timed movement of plate 29 can be utilized to initiate final arming of missile M. For example, movement of rod 21 can be utilized to drive an arming rotor or to connect certain switch contacts which accomplish final `arming of the missile warhead.

It will be apparent that the embodiments shown are only exemplary and that various modifications can be made in construction and arrangement within the scope of the invention as defined in the appended claims.

We claim as our invention:

l. In combination, a missile, a detonator in said missile adapted to initiate detonation thereof, and means for initiating detonation of said detonator some predetermined time `after the missile has been launched, said means comprising in combination: a thermal motor, said thermal motor comprising; a heat conductor having iirst and second heat conducting portions, the lirst portion being flush with the outer surface of said missile and the second portion extending from said first port-ion into said missile; an expansible bellows surrounding said second portion and sealed at one end to said first portion; a circular plate sealing the other end of said bellows, said circular plate being movable in a first direction; a vaporizable liquid encapsulated in said bellows, said liquid being selected so that a given quantity of heat conducted by said heat conductor to said liquid causes said liquid to develop a vapor pressure sufficient to expand said bellows and drive said plate in said first direction, said given quantity of heat conducted to said liquid by said heat conductor being created in said heat conductor as a result of missile flight for some predetermined period of time; and means associated with said plate and adapted to initiate detonation of said detonator when said plate is driven in said first direction.

2. In combination, a missile, a detonator in said missile adapted to initiate detonation thereof, and means for initiating detonation of said detonator some predetermined time after the missile has been launched, said means comprising in combination: a thermal motor, said thermal motor comprising; a heat conductor having first and second heat conducting portions, the first portion being flush with the outer surface of said missile and the second portion extending from said first portion into said missile; anV expansible bellows surrounding said second portion and sealed at one end to said first portion, a circular plate sealing Ithe other end of said bellows, said circular plate being movable in a first direction, a vaporizable liquid encapsulated in said bellows, said liquid being selected so that a given quantity of heat conducted by said heat conductor to said liquid causes said liquid to develop a vapor pressure sufhcient to expand said bellows and drive said plate in said rst direction, said given quantity of heat conducted to said liquid by said heat conductor being created in said heat conductor as a result of missile iiight for so-rne predetermined period of time; means yassociated with said plate and adapted to initiate said detonator when said plate is driven in said first direction; and adjustable means adapted to restrain driving movement of said plate in said first direction, thereby varying the time required before the vapor pressure in said thermal motor develops suiiiciently to drive said plate.

3. In combination, a missile, a detonator in said missile adapted to initiate detonation thereof, and means for initiating detonation of said detonator some predetermined time after the missile has been launched, said means y comprising in combination: a thermal motor, said thermal motor comprising; a heat conductor consisting of a substantially iiat circular plate and a cylindrical cup extending from said plate, said plate being fixed toV said missile with its outermost surface flush with the outer surface of said missile, said cylindrical cup being connected at its outermost end to the innermost surface of the xed plate and extending inwardly into said missile, the longitudinal axis of said cylindrical cup being substantially perpendicular to the longitudinal axis of said missile, an expansible, substantially cylindrical bellows encasing the outer periphery of said cylindrical cup with its longitudinal axis substantially coaxial to the longitudinal axis of said cylindrical cup, the outermost end of said bellows being sealed to the innermost surface of said fixed plate, a movable plate adjacent the innermost end of said cylindrical cup, the innermost end of said bellows being sealed to said movable plate so that a vapor-tight seal exists between said heat conductor and said movable plate, said movable plate being movable in a direction parallel to said longitudinal axis of said cylindrical cup, a vaporizable liquid encapsulated in said bellows, said liquid being selected so that a given quantity of heat conducted to said liquid by said heat conductor causes said liquid to develop a vapor pressure suicient to expand said bellows and drive said movable plate in a first direction, said given quantity of heat conducted to said liquid by said cylindrical cup being created in said outermost surface of said fixed plate as a result of missile ight for some predetermined period of time; and means associated with said plate and adapted to initiate detonation of said detonator when said plate is driven in said first direction.

4. In combination, a missile, a detonator in said missile adapted to initiate detonation thereof, and means for initiating detonation of said detonator some predetermined time after the missile has been launched, said means comprising in combination: a thermal motor, said thermal motor comprising; a heat conductor consisting of a substantially at circular plate and a cylindrical cup extending from said plate, said plate being xed to said missile with its outermost surface ush with the outer surface of said missile, said cylindrical cup being connected at its outermost end to the innermost surface of the fixed plate and extending inwardly into said missile with its longitudinal axis substantially perpendicular to the longitudinal axis of said missile, an expansible, substantially cylindrical bellows encasing the outer periphery of said cylindrical cup with its longitudinal axis substantially coaxial to the longitudinal axis of said cylindrical cup, the outermost end of said bellows being sealed to the innermost surface of said fixed plate, a movable plate adjacent the innermost end of said cylindrical cup, the innermost end of said bellows being sealed to said movable plate so that a vapor-tight seal exists between said heat conductor and said movable plate, said movable plate being movable in a direction parallel to said longitudinal axis of said cylindrical cup, a vaporizable liquid encapsulated in said bellows, said liquid being selected so that a given quantity of heat conducted to said liquid by said heat conducted to said liquid by said heat conductor causes said liquid to develop a vapor pressure sufficient to expand said bellows and drive said movable plate in a rst direction, said given quantity of heat conducted to said liquid by said cylindrical cup being created in said outermost surface of said fixed plate as a result of missile flight for some predetermined period of time; means associated with said plate and adapted to initiate detonation of said detonator when said plate is driven in said lirst direction; and adjustable means adapted to restrain driving movement of said plate in said first direction, thereby varying the time required before the vapor pressure in said thermal motor develops sufliciently Ito drive said movable plate.

No references cited. 

